Lecture 3
TCP/IP & the Internet
Boriana Koleva
Room: C54
Email: bnk@cs.nott.ac.uk
Overview
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Protocol design
Overview of TCP/IP
IP addresses and domain names
‘Warriors of the net’ video
Network Protocols
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Communication hardware transfers raw data
(i.e. a steam of bits)
Usually more sophisticated instructions need to
be sent over networks
This requires software which needs to follow
standards for interoperability
Protocols are the rules that govern
communication on networks
Protocols are implemented by protocol software
Stacks of Layers
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Protocols are designed according to a layered model
The protocol software on each computer is divided
into modules – each corresponding with a layer
Each module only communicates with the modules
corresponding to the layer above and the layer below
All the protocol modules on a computer are
collectively called a stack or suite
Network communication requires that the same stack
is installed on all computers (though the hardware
and OS may be different)
The Layering Principle
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Layer N software on the destination
computer must receive the exact
message sent by layer N software on the
sending computer
Examples of Protocol Stacks
Vendor
Novell
Stack
Netware
Apple
Appletalk
IBM
SNA
Various (Internet)
TCP/IP
Internet Reference Model
(TCP/IP)
TCP/IP
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Protocol stack used by the Internet
Originally designed for DARPA (late 1960’s)
Major design features intended for military use
• Multiple contractors
• Simple (basic services)
• Robust - automatic recovery from battlefield damage
These same features make the Internet possible
• Multiple vendors
• Simple (basic services)
• Robust - the Internet is not centrally coordinated
Since early 1980’s TCP/IP has been built into Unix
Now available for, or as part of all major OS
The Internet
A vast network
of networks
Virtual network
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TCP/IP gives illusion that
there is a single universal
network
Universal service - any two
computers should be able to
communicate
Hardware: routers connect
different networks
Internet protocols: provide
universal service by creating a
single virtual network
TCP/IP Jargon (1)
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Host - any system that connects to an Internet
and that runs applications
Router - a device that connects independent
networks together to form an internetwork
• Forwards packets from one network to another
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Both hosts and routers use TCP/IP protocol
software
Sockets - the API for TCP/IP software (i.e. the
library of functions that a program can use to
access TCP/IP facilities)
• For example the Winsock API on Windows
TCP/IP Jargon (2)
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Host Name
• all hosts on a TCP/IP network must have a unique name
• this may be a single word (on a small network) or follow a
hierarchical convention
Internet Address (IP Number)
• all hosts on the Internet must have a unique identifying
number
• 32-bit number, usually written as 4 bytes separated by dots
(e.g. 128.243.20.172)
Ethernet Address (Media Access Control, MAC)
• a unique number built into each Ethernet subsystem by the
manufacturer
• 6-byte numbers, usually written in hex separated by dashes
(e.g. 02-FE-87-4A-8C-A9)
• if Ethernet is not used (e.g. over a phone line) then the
software stack must provide a MAC
IP (Internet Protocol)
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Layer 3 protocol
A packet switching protocol
• packets of data are routed between nodes with no
previously established path
• connectionless
IP is responsible for moving packet of data from machine to
machine
• IP forwards each packet based on a four byte destination
address (the IP number)
• The Internet authorities assign ranges of numbers to
different organisations
• Organisations assign their own subsets of numbers to
departments
• IP operates on routers that move data from LANs to WANs
and global WANs
TCP (Transport Control Protocol)
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Layer 4 protocol
Connection-oriented
Data may be sent in a continual stream
between two hosts
TCP is responsible for verifying the correct
delivery of data between machines
• detection of errors or lost data
• management of retransmission until the data is
correct and completely received
• assembles packets of data into the correct order
without duplication
• handles multiplexing
IP Numbers
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IP number is a unique identifier for TCP/IP
• Analogous to telephone number
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IP numbers consist of 4 bytes (i.e. numbers from
0-255)
• This gives a maximum of 2554 (4,294,967,296)
• Dotted decimal notation for human readability
• 128.242.22.17
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Each 32 bit address is divided into two parts:
• prefix: physical network to which the host is
attached - the network number
• suffix: a host attached to a given physical network
Classes of IP address
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Size of prefix and suffix determines maximum number of
networks and maximum number of hosts per network
TCP/IP networks are usually class C
• Class C networks
• Suitable for small organisations
• First three bytes identify the network
• The last byte identifies hosts (i.e. maximum of 256)
• Class B networks
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Suitable for large organisations
First two bytes identify the network
The last two bytes identifies hosts (i.e. maximum of 65,536)
Class B networks are usually divided into subnets (i.e. a
maximum of 256 subnets, each containing up to 256 hosts)
• Class A networks
• First byte identifies the network
• Major networks (e.g. JANET)
Special IP Numbers
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Some IP numbers have special meanings,
and so are not normally assigned to
individual hosts
Broadcast Address – 255
• Listened to by all machines on the network
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Loopback Network – 127
• 127.0.0.1 - loopback address (localhost)
Host & Domain Names
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Domain names are alphanumeric labels assigned to IP
numbers
Each host name on a subnet must be unique
There is a hierarchy of domain names
• Top level
• Country (if not US) – e.g. UK, FR, IE
• Category - COM, MIL, GOV, EDU, ORG etc (or CO.UK, AC.UK,
GOV.UK, ORG.UK etc)
• NB domain registration does not necessarily correspond to
physical location!
• Second level
• Organisation (e.g. NOTT.AC.UK)
• Third level
• Subnet (e.g. CS.NOTT.AC.UK)
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Host names may be aliased
Host names are obtained from databases called nameservers
IP Numbers and domain names
– a Nottingham Example
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JANET (Joint Academic Network)
• *.uk.ac
• 128.*.*.*
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University of Nottingham (Class B network)
• *.nott.ac.uk (also aliases – e.g. *.nottingham.ac.
• 128.243.*.*
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Computer Science
• *.cs.nott.ac.uk
• 128.243.20.* 128.243.21.*
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Marian (Unix server)
• marian.cs.nott.ac.uk
• 128.243.21.16
128.243.22.*
Domain name conversion
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Fully qualified domain names must be converted
to IP numbers before communication can take
place over the Internet
• DNS servers
Summary
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Protocol design
TCP/IP overview
IP addresses and domain names